There are a number of medical conditions for which it has been found that an effective therapy involves driving current through a section of the tissue of a patient. Often, the current is driven between the electrodes of an electrode array implanted in the patient. Generally, the electrode array includes a non-conductive carrier on which typically two or more electrodes are disposed. Once the electrode array is implanted, current is driven from at least one of the electrodes, through the adjacent tissue, to at least one of the other electrodes. The current flow through the tissue influences the tissue to accomplish a desired therapeutic result. For example, an electrode array positioned adjacent the heart may flow currents to stimulate the appropriate contraction and expansion of the heart muscles. There is an increasing interest in implanting electrode arrays adjacent neural tissue so that the resultant current flow induces a desired neurological or physical effect. In one known application, the current driven between the electrodes of an array placed on top of the dura in the vertebral column reduces the extent to which chronic pain signals are perceived by the brain. Alternatively, the array may be placed in a location where the current flow stimulates a feeling of stomach fullness as part of an appetite suppression/weight management therapy. In another application, the current is flowed to tissue or nerves associated with the bladder or the anal sphincter to assist in control of incontinence. Electrodes may be implanted in a paralysis victim to provide muscle control and/or a sense of feeling.
The Applicants' Patent Application No. PCT/US2009/33769, FOLDABLE, IMPLANTABLE ELECTRODE ARRAY ASSEMBLY AND TOOL FOR IMPLANTING SAME, filed 11 Feb. 2009, published as WO 2009/111142 and as U.S. Pat. Pub. No. US 2011/0077660 A1, the contents of which are explicitly incorporated herein by reference, describes an electrode array that includes a frame on which plural electrodes are arranged in a row by column matrix. An advantage of this electrode array is that it allows current to be flowed between numerous different combinations of electrodes. Depending on which electrodes are operated to function as current sources and sinks, this array can be operated so that there are two or more current flows occurring simultaneously between different sets of electrodes. Once this array is deployed, the practitioner drives current between different combinations of electrodes. Current therefore flows through different sections of tissue. This allows the practitioner to determine between which electrodes, through which tissue, the current flow offers the greatest benefit and/or tolerable side effects. Once the optimal current flow path between the electrodes is determined, the array and its associated power supply are set to operate in this state. Should the electrodes shift or the clinical needs change, the array can be reset to accommodate these changes.
In comparison to other electrode arrays with lesser numbers of electrodes, the above-described array makes it possible to flow current through more discretely targeted sections of tissue and to selectively focus/diffuse the current flow. In contrast to an electrode array with a smaller number of electrodes, use of the above-described array increases the likelihood that the current flow can be set to provide desired therapeutic effects, with tolerable side effects.
Previously, there was a disadvantage of providing an electrode array with numerous individual electrodes that collectively occupy a large surface area. Specifically, owing to the size of these arrays, it was believed that the only way to position them against the tissue through which current is to be driven was to cut a relatively large incision in the patient to provide access to the target tissue. Typically, this incision is more than 3 cm in length and, often at least 5 cm in length. Once the incision is made, it is then usually necessary to retract at least a portion of the tissue overlying the target tissue. In some insertion procedures, removal of some of the overlying tissue is required. The electrode array was passed through the incision and placed against the target tissue. Once the electrode array was positioned, the incision was closed.
The electrode array of the incorporated by reference WO 2009/111142, is designed in part to be implanted in a patient without requiring such a large sized incision, tissue removal and the attendant trauma that results from these procedures. The Applicants' array of this incorporated-by-reference document is designed so that the electrodes are disposed on a frame formed from a superelastic material. A superelastic material is one that, after being subjected to appreciable bending or folding, returns to its initial state. Once this electrode array is formed, the assembly is then folded or rolled into a form that has a side-to-side width appreciably less than its width in the unfolded/unrolled state.
The Applicant's PCT Pat. App. No. PCT No. PCT/US2010/029628, published as US 2012/0022551 A1, DELIVERY ASSEMBLY FOR PERCUTANEOUSLY DELIVERING AND DEPLOYING AN ELECTRODE ARRAY AT A TARGET LOCATION, THE ASSEMBLY CAPABLE OF STEERING THE ELECTRODE ARRAY TO THE TARGET LOCATION, filed 1 Apr. 2010, the contents of which are incorporated herein by reference, discloses how a foldable electrode array can be folded around a core. The core and folded over array are encased in a sheath. Steering cables are encased in the sheath. The assembly of this invention is designed to be advanced through a portal formed in the patient. From the portal, the assembly is advanced through a potential space in the patient to the target location where the array is to be deployed. Tensions are selectively imposed on the steering cables to steer the sheath. This steering is necessary to direct the sheath, and the components encased therein, around obstructions so the sheath and encased components can be pushed to the target location. The sheath is considered at the target location when the distal end of the sheath, the section holding the folded electrode array, is disposed over the tissue against which the array is to be deployed. Once the sheath is at the target location, the sheath is retracted away from the electrode array and the core. The retraction of the sheath allows the release of the potential energy of the material forming the array frame. The release of this energy unfolds the array from around the core so the array is disposed against the target tissue. At this stage of the deployment process, the core remains between the array and the tissue against which the array is to be deployed. The core is retracted away of the unfolded electrode array. The array therefore seats against underlying tissue. Once the array is so seated, the array is considered completely deployed and ready for use.
Applicant's PCT Pat. App. No. PCT No. PCT/US2010/029628 discloses how a folded over array can be steered to a location over the tissue against which the array is to be deployed. However, this document does not teach: how the folded over array is initially percutaneously inserted in the patient; how the array is initially positioned in the proper orientation for advancement to the target location; or the structure of tool that can be used to both advance the sheath-encased array to the target location while steering the array. Also, the prior application does not disclose tools that can be used to first retract the sheath away from the array and then retract the core from out from underneath the folded over array.